Semiconductor lasers which provide lateral confinement for the injection current are well know. Buried waveguide, also known as buried heterostructure, semiconductor lasers are e.g. well known per se, i.a. from U.S. Pat. No. 5,277,015, U.S. Pat. No. 5,260,230, U.S. Pat. No. 5,398,255, U.S. Pat. No. 5,452,315, and U.S. Pat. No. 5,470,785. Both ridge waveguide and buried waveguide lasers are known to yield lateral control of electrical and optical confinement.
By lateral direction, a direction perpendicular to the direction of epitaxial growth, is to be understood. For VCSELs (Vertical Cavity Surface Emitting Lasers), the lateral direction may denote all directions in the plane perpendicular to the growth direction. For EELs (Edge Emitting Lasers), the lateral direction is usually perpendicular to the direction of propagation of lasing light. Furthermore, electrical lateral confinement denotes the control of spread of injection current in the lateral direction, while optical lateral confinement denotes the waeguide lateral control of the lasing light.
For ridge waveguide lasers, a ridge (or mesa) is formed above the active region, where the active region in the vicinity of lasing action, is not constricted in the lateral direction. The electrical lateral confinement is achieved by the finite spread of injection current in the active layer, due to the finite width of the above ridge The optical lateral confinement is obtained by the waveguiding due to the ridge. For buried waveguide lasers, the active layer is laterally constructed by (i.e. included in) the mesa. The mesa is epitaxially buried in order to avoid deteriorated performance caused by crystal imperfections in the vicinity of the active lasing regions. The electrical and optical lateral confinement, respectively, is obtained by the difference between active and burying material, in band offset and refractive index, respectively.
However, for ordinary ridge and buried waveguide lasers, both electrical and optical lateral confinement are controlled with the same design parameters, i.e. physical dimensions and material of the mesa, active layer and burying material.